Polymer-based paint compositions suitable to be sprayed from pressurized aerosol containers are desirably formulated so that objectionable foaming of the dispensed paint film does not occur. Foaming results in marring or pocking of the dried polymer-pigment film.
In addition, the paint formulation which is dispensed from an aerosol container should be of sufficient mechanical stability to withstand the mechanical shearing forces which occur during dispensing from a conventional aerosol container. Aerosol formulations having insufficient mechanical stability produce films having an uneven surface marred by agglomerated bits of the polymeric component or formulations which clog the narrow orifices in the aerosol valve outlet.
Currently marketed aerosol paints having appropriate mechanical stability are entirely solvent-based systems, employing hydrocarbon- or alcohol-based solvents which employ little, if any, water. In such formulations, the polymer-pigment concentrate may be formulated in a liquid hydrocarbon, such as kerosene, and propelled by a kerosene soluble propellant such as isobutane, or a fluorocarbon. It is necessary to maintain a low viscosity in polymer-pigment concentrates in order to provide rapid escape of the propellant from the film, thus eliminating foam-pocking, and providing a coherent and even layer of the polymeric component of the aerosol formulation. Although such solvent-based systems can be formulated to suppress foaming upon spray application, alcohol- or hydrocarbon-based concentrates are disadvantageous due to their high flammability and/or high toxicity. Aerosol-dispensed paint compositions in which the sprayable concentrate is a polymer-in-water emulsion would ameliorate many of the disadvantages associated with the use of toxic and flammable alcohol- or hydro-carbon-based paint sprays.
In light of the environmental hazards associated with aerosol propellants such as the commonly employed fluorocarbon propellants, it is also important to employ a propellant which is environmentally safe. The propellant dimethyl ether is environmentally safe and also possesses a low flammability when used in combination with water. However, the prior art does not disclose dimethyl ether-propelled, water-based polymer emulsions suitable for use as aerosol dispensed film-formers which are free of objectionable foaming upon spraying and at the same time possess the degree of mechanical stability required for aerosol dispensed formulations.
Accordingly, it is an object of the present invention to provide a dimethyl ether-propelled aqueous polymer emulsion which will deliver a smooth and unfoamed film when applied to a substrate from a conventional aerosol dispenser. The formulations of this invention are well suited for use as aerosol water-based paints and for this purpose may be formulated with conventional pigments.
It is another object of this invention to provide an aerosol dispenser containing the composition of this invention which dispenses an aqueous polymer emulsion so as to provide a smooth, unpocked film on the surface to which it is applied.